Wear resistant lathe bed scanning apparatus and method

ABSTRACT

A lathe bed scanning apparatus and method has a wear resistant coating on translational rod bearings which support a scanner for slidable movement in a frame. Titanium nitride is coated over a hardened stainless steel core of the translational rods and bearing pads which are arranged for sliding contact with the rods comprise diamond laminated tungsten carbide.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. Ser. No. 08/621,417 entitled "ANAPPARATUS FOR PREVENTING AXIAL MOVEMENT OF A LEAD SCREW" by Roger S.Kerr et al.

FIELD OF THE INVENTION

This invention relates generally to the field of lathe bed scannersutilizing a frictionless bearing pad, more particularly, to africtionless bearing pad coupled with a wear resistant translational rodbearings.

BACKGROUND OF THE INVENTION

Color-proofing is the procedure used by the printing industry forcreating representative images that replicate the appearance of printedimages without the cost and time required to actually set up ahigh-speed, high-volume printing press to print an example of the imagesintended. One such color proofer is a lathe bed scanner which utilizes athermal printer having half-tone capabilities. This printer is arrangedto form an image on a thermal print medium, or writing element, in whicha donor transfers a dye to the thermal print medium upon a sufficientamount of thermal energy. This printer includes a plurality of diodelasers which can be individually modulated to supply energy to selectedareas of the medium in accordance with an information signal. Theprint-head of the printer includes one end of a fiber optic array havinga plurality of optical fibers coupled to the diode lasers. The thermalprint medium is supported on a rotatable imaging drum, and theprint-head with the fiber optic array is movable relative to thelongitudinal axis of the drum. The dye is transferred to the thermalprint medium as the radiation, transferred from the diode lasers to thedonor element by the optical fibers, is converted to thermal energy inthe donor element.

For permitting relative movement of the print-head, the print-head ismounted on a translation table which, in turn, is attached to arotatable lead screw having a threaded shaft. The lead screw restsbetween two sides of the frame of the scanner where it is supported onboth ends by bearings. At the drive end, the lead screw continuesthrough the bearing, through a pair of spring retainers that areseparated and loaded by a compression spring and to a drive motor. Thedrive motor induces rotation to the screw, and the compression springfunctions to limit axial movement of the lead screw.

The print-head moves in accordance with the translation table which, inturn, moves axially along translational rod bearings in register withthe media during the write process. To ensure proper image quality, themovement of the table, and hence the printhead, must be precise andsmooth. To achieve smooth translation, the current systems make use ofbearing pads embedded in the bottom of the translation table that makecontact with the translational rod bearings thereby reducing frictionbetween the table and the bearing shafts. These pads are made from acommercially available plastic Delrin™ and the bearings are made fromAISI 400 series stainless steel. This bearing apparatus is inadequatebecause it has significant friction which results in premature wear andconsequently costly service and calibration.

There have been numerous attempts to solve the above friction and wearproblems. For instance, U.S. Pat. No. 4,764,036 discloses tungstencarbide (WC) radial bearing or thrust inserts. The entire assembly isused as a hydrodynamic bearing in contrast to our invention asfrictionless or rather low friction slide bearing. Further, U.S. Pat.No. 4,522,453 relates to the use of PVD (physical vapor deposition) andCVD (chemical vapor deposition) coatings comprising borides, nitridesand carbides as corrosion resistant as well as protection against hightemperature wear. Moreover, U.S. Pat. No. 4,404,598 describesconstruction of engraving machines comprising lightweight lathe bedconfigurations. Low coefficient of friction Nylatron™ plastic pads areused on which rides the carriage.

Although the presently known and utilized scanner is satisfactory, it isnot without shortcomings. The Delrin™ pads and the translational rodbearings are subjected to wear and abrasion and consequently requirefrequent maintenance and replacement. This is obviously labor intensive,time consuming and expensive.

Consequently, a need exists for improvements in the construction of thelathe bed scanner so as to overcome the above-described shortcomings.

SUMMARY OF THE INVENTION

The present invention is directed to overcoming one or more of theproblems set forth above. Briefly summarized, according to one aspect ofthe present invention, a wear resistant lathe bed scanning apparatus hasa frame and a scanning means mounted for slidable movement in the frame.The scanning means has first and second end portions. A firsttranslational rod bearing supports the first end portion of scanningmeans for slidable movement relative to the frame. The firsttranslational rod bearing is in sliding contact with a first bearing padassembly arranged in the first end portion of the scanning means.Further, a second translational rod bearing cooperatively associatedwith the first translational rod bearing supports the second end portionof the scanning means for slidable movement in the frame. Similarly, thesecond translational rod bearing is arranged in sliding contact with asecond bearing pad assembly arranged in the second end portion of thescanning means. Each of the first and second translational rod bearingscomprises a central core of heardenable stainless steel and a hard wearresistant coating on the central core. Moreover, each of the first andsecond bearing pad assemblies comprises at least one bearing pad whichcomprises a laminate having a first innermost layer of tungsten carbideand a second outermost layer of a crystalline carbon material laminatedto the first innermost layer. The second outermost layer of the firstand second bearing pads define a bearing contact surface. Further, drivemeans operably connected to the scanning means provides movement of thescanning means along the first and second translational rod bearingsrelative to the frame.

It is, therefore, an object of the invention to provide a lathe bedscanning apparatus and method that is wear resistant and durable.

It is another object of the present invention to provide bearing padswhich have a very low coefficient of friction when they come in contactwith another moving member to overcome the above-described drawbacks.

It is another object of the present invention to make the translationalrod bearings more wear resistant by coating with a hard material.

It is an advantage of the present invention to provide improvedreliability of the bearing pad aid translational rod bearing assembly;

It is an advantage of the present invention to eliminate or reduce weardue to excessive friction between the pad and the translational rodbearings,

It is an advantage of the present invention to provide a frictionlesspad and translational rod bearing assembly that reduces or eliminatesthe need for calibration.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects of the present invention will becomeapparent when taken in con junction with the following description anddrawings wherein identical reference numerals have been used, wherepossible, to designate identical elements that are common to thefigures, to wit:

FIG. 1 is a side view in vertical cross section of an image processingapparatus of the present invention;

FIG. 2 is a perspective of the lathe bed scanning subsystem or writeengine of the present invention;

FIG. 3 is a cross-sectional side view of the translation table for thepresent invention;

FIG. 4 is a cross-sectional view of the bearing pad of the presentinvention, and

FIG. 5 is a fragmented cross-sectional view of the translational rodbearing.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, there is illustrated an image processing apparatus10 according to the present invention having an image processor housing12 for forming a protective cover. A movable, hinged image processordoor 14 is attached to the front portion of the image processor housing12 for permitting access to two sheet material trays, lower sheetmaterial tray 50a and upper sheet material tray 50b, that are positionedin the interior portion of the image processor housing 12 for supportingthermal print media 32 thereon. It will be obvious to those skilled inthe art that only one of the sheet material trays 50 will dispense thethermal print media 32 out of its sheet material tray 50 to create anintended image thereon; the alternate sheet material tray 50 eitherholds an alternative type of thermal print media 32 or functions as aback up. In this regard, the lower sheet material tray 50a includes alower media lift cam 52a for lifting the lower sheet material tray 50aand ultimately the thermal print media 32 upwardly toward a rotatable,lower media roller 54a and, ultimately, toward a second rotatable, uppermedia roller 54b which, when both are rotated, permit the thermal printmedia 32 to be pulled upwardly towards a media guide 56. The upper sheetmaterial tray 50b includes a upper media lift cam 52b for lifting theupper sheet material tray 50b and ultimately the thermal print media 32towards the upper media roller 54b which directs it towards the mediaguide 56.

The movable media guide 56 directs the thermal print media 32 under apair of media guide rollers 58 which engages the thermal print media 32for assisting the upper media roller 54b in directing it onto the mediastaging tray 60. The media guide 56 is attached and hinged to theinterior of the housing 12 at one end, and is uninhibited at its otherend for permitting multiple positioning of the media guide 56. The mediaguide 56 then rotates its uninhibited end downwardly, as illustrated inthe position shown, and the direction of rotation of the upper mediaroller 54b is reversed for forcing the thermal print medium receiversheet material 32 resting on the media staging tray 60 under the pair ofmedia guide rollers 58, upwardly through an entrance passageway 204 andaround a rotatable vacuum imaging drum 300.

A roll of dye donor material 34 is connected to the media carousel 100in a lower portion of the image processor housing 12. Four rolls areused, but only one is shown for clarity. Each roll includes a dye donormaterial 34 of a different color, typically black, yellow, magenta andcyan. These dye donor materials 34 arc ultimately cut into dye donorsheet materials and passed to the vacuum imaging drum 300 for formingthe medium from which dyes imbedded therein are passed to the thermalprint media 32 resting thereon, which process is described in detailherein below. In this regard, a media drive mechanism 110 is attached toeach roll of dye donor material 34, and includes three media driverollers 112 through which the dye donor material 34 of interest ismetered upwardly into a media knife assembly 120. After the dye donormaterial 34 reaches a predetermined position, the media drive rollers112 cease driving the dye donor material 34 and the two media knifeblades 122 positioned at the bottom portion of the media knife assembly120 cut the dye donor material 34 into dye donor sheet materials. Themedia rollers 54 and media guide 56 then pass the dye donor sheetmaterial onto the media staging tray 60 and ultimately to the vacuumimaging drum 300 and in registration with the thermal print media 32using the same process as described above for passing the thermal printmedia 32 onto the vacuum imaging drum 300. The dye donor sheet materialnow rests atop the thermal print media 32 with a narrow gap between thetwo created by microbeads imbedded into the thermal print media 32.

A laser assembly 400 includes a quantity of laser diodes 402 in itsinterior portion, and these lasers 402 are connected via fiber opticcables 404 to a distribution block 406 and ultimately to the printhead500. The printhead 500 directs thermal energy received from the laserdiodes 402 for causing the dye donor sheet material to pass the desiredcolor of dye across the gap to the thermal print media 32. The printhead500 is attached to a lead screw 250 via a lead screw drive nut 254 (notshown in FIG. 1) for permitting movement axially along the longitudinalaxis of the vacuum imaging drum 300 for transferring the data to createthe intended image onto the thermal print media 32.

For writing, the vacuum imaging drum 300 rotates at a constant velocity,and the printhead 500 begins at one end of the thermal print media 32and traverses the entire length of the thermal print media 32 forcompleting the transfer process for the particular dye donor sheetmaterial 34 resting on the thermal print media 32. After the printhead510 has completed the transfer process, the particular dye donor sheetmaterial resting on the thermal print media 32 is then removed from thevacuum imaging drum 300 and transferred out the image processor housing12 via a skive or ejection chute 16. The dye donor sheet materialeventually comes to rest in a waste bin 18 for removal by the user. Theabove described process is then repeated for the other three rolls 30 ofdye donor materials 34.

After the color from all four sheets of the dye donor sheet materials 34have been transferred, the thermal print media 32 is transported via atransport mechanism 80 through an entrance door 182 to a color bindingassembly 180. The entrance door 182 is opened for permitting the thermalprint media 32 to enter the color binding assembly 180, and shuts oncethe thermal print media 32 comes to rest in the color binding assembly180. The color binding assembly 180 processes the thermal print media 32for further binding the transferred colors on the thermal print media 32and for sealing the microbeads thereon. After the color binding processhas been completed, a media exit door 184 is opened and the thermalprint media 32 with the intended image thereon passes out of the colorbinding assembly 180 and the image processor housing 12 and comes torest against a media stop 20.

Referring to FIG. 2, there is illustrated a perspective of the lathe bedscanning subsystem 200 of the image processing apparatus 10, includingthe vacuum imaging drum 300, printhead 500 and lead screw 250 assembledin the lathe bed scanning frame 202. The vacuum imaging drum 300 ismounted for rotation about an axis X in the lathe bed scanning fra me202. The printhead 500 is movable with respect to the vacuum imagingdrum 300, and is arranged to direct a beam of light to the dye donorsheet material (shown in FIG. 1). The beam of light from the printhead500 for each laser diode 402 (not shown in FIG. 2) is modulatedindividually by modulated electronic signals from the image processingapparatus 10, which signals are representative of the shape and color ofthe original image, so that the color on the dye donor sheet material 34is heated to cause volatilization only in those areas in which itspresence is required on the thermal print media 32 to reconstruct theshape and color of the original image.

The printhead 500 is mounted on a movable translation platform 220which, in turn, is supported for low friction slidable movement ontranslational rod bearings 206 and 208. The translational rod bearings206 and 208 are sufficiently rigid so that they do not sag or distortbetween their mounting points and are arranged as parallel as possiblewith the axis X of the vacuum imaging drum 300 with the axis of theprinthead 500 perpendicular to the axis X of the vacuum imaging drum 300axis. The front translational rod bearing 208 locates the translationplatform 220 in the vertical and the horizontal directions with respectto axis X of the vacuum imaging drum 300. The rear translational rodbearing 206 locates the translation platform 220 only with respect torotation of the translation platform 220 about the front translationalrod bearing 208 so that there is no over-constraint condition of thetranslation platform 220 which might cause it to bind, chatter, orotherwise impart undesirable vibration or jitters to the printhead 500during the generation of an intended image.

Referring to FIG. 3, there is illustrated a partial verticalcross-sectional view of the lathe bed scanning subsystem comprising analternative embodiment of the front translational rod bearing 208, reartranslational rod bearing 206, front bearing pad assembly 610 and therear pad bearing 660 of the present invention. It is to be noted thatthe front and rear translational rod bearings as well as the bearing-padassemblies have identical functions although the bearing pad assembliesdiffer in design and physical dimensions.

Referring to FIG. 4, the alternative embodiment of the frictionlessfront bearing pad assembly 610 comprises the use of a tungsten carbide(WC) substrate 614 having thickness ranging from 5 to 50 mm, laminatedwith sintered industrial grade sintered diamond wafer 616 havingthickness ranging from 1 to 5 mm. The diamond laminated WC bearing padis fastened to the bearing pad housing 620 or attached by shrink fittingas is well known to the artisans. The WC substrate is made usingparticulate WC powder mixed with Co or Ni metal in the range of 2 to 20%by weight. The preferred Co or Ni concentration is 6% by weight. Themechanical mixture of ceramic WC and the metal Co or Ni is known as"cermet" to the artisans. WC cermet substrates having simple shapes canbe made by dry pressing the cermet powder mixed with 2 to 5 weight %organic binder such as polyvinyl alcohol, polyvinyl acetate, orpolyethylene glycol using uniaxial pressure of 6,000 to 20,000 psi,preferably 10,000 psi. The pressed substrate is sintered preferably in avacuum furnace at 1600° to 1900° C., preferably at 1750° C. Thesintering schedule includes heating the substrate in vacuum of 1×10⁻⁵ to5×10⁻⁶ Torr from room temperature to 500° C. at 5° C. per minute, from500° C. to 1750° C. at 12° C. per minute, sintering at a holdingtemperature of 1750° C. for at least 1 hour and then cooled to roomtemperature at 15° C. per minute. The sintered substrate attains 95 to99% of the theoretical density. The average particle size of WC powderranges from 0.5 to 5 μm, the preferred particle size being 1μm. Sintereddiamond laminates are obtained from Smith Tool Co or Norton. The diamondlaminate 616 is brazed to the WC substrate using Ag--Cu or Ag--Cu--Tialloy at 750° to 820° C. in vacuum. The brazing material 612 used wasCerametel 721™ manufactured by Lucas-Milhaupt, Inc at Wisconsin. Thebrazing material Cerametel 721™ comprises 72 weight % silver and 28weight % copper. A foil of the brazing material 612 was sandwichedbetween the diamond wafer 616 and a WC substrate 614 and fixtured suchthat the assembly does not move during the heating process. The brazingassembly was placed inside a vacuum furnace and the furnace wasevacuated to 10⁻⁵ Torr. The furnace was then backfilled with Ar gas andthe furnace was heated to 700° C. at a rate of 50° C. per minute. Afterthe furnace attained the temperature 700° C. and stabilized, the brazingassembly was heated again to 780° to 800° C., preferably at 785° C. for5 minutes and then the furnace was cooled to room temperature at 30° C.per minute. The bearing pad assembly was then attached to the housing620 as described earlier. Alternatively, the diamond laminate 616 can bebonded to the WC substrate 614 using high strength epoxy resins.Referring to FIG. 3 again, the rear and front translational rod bearings206 and 208, respectively are made from hardenable AISI 400 seriesstainless steel (hardness: Rockwell C 58 to 60) and coated with titaniumnitride coating. Alternatively, the translational rod bearings 206, 208can also be coated with hard and wear resistant titanium carbonitride,Ti(C,N) coating.

Referring to FIG. 5, the translational rod bearing 206 is coated withwear resistant TiN coating 350 having thickness ranging from 3 to 5 μm.The TiN coating is deposited using a PVD (physical vapor deposition)process. Ion plating is a preferred PVD process which is well known tothe artisans. Simply stated, the process involves evaporating titaniummetal with an electron beam in a vacuum chamber in a nitrogen-argonplasma whereby vaporized Ti is ionized by the plasma and combine withnitrogen ions to form TiN on the substrate which is biased negatively.

It will be obvious to those skilled in the art that by providing lowfriction and wear resistant bearing pads in conjunction with wearresistant translational rod bearings, the translation motion will besmooth and consistent.

The invention has been described with reference to the preferredembodiment thereof. However, it will be appreciated and understood thatvariations and modifications can be effected within the spirit and scopeof the invention as described herein above and as defined in theappended claims, by a person of ordinary skill in the art withoutdeparting from the scope of the invention.

PARTS LIST

10 Image processing apparatus

12 Image processor housing

14 Image processor door

16 Donor ejection chute

18. Donor waste bin

20 Media stop

32 Thermal print media

34 Dye donor roll material

50 Sheet material trays

50a Lower sheet material tray

50b Upper sheet material tray

52 Media lift cams

52a Lower media lift cam

52b Upper media lift cam

54 Media rollers

54a Lower media roller

54b Upper media roller

56 Media guide

58 Media guide rollers

60 Media staging tray

80 Transport mechanism

100 Media carousel

110 Media drive mechanism

112 Media drive rollers

120 Media knife assembly

122 Media knife blades

180 Color binding assembly

182 Media entrance door

184. Media exit door

200 Lathe bed scanning subsystem

202 Lathe bed scanning frame

204 Entrance passageway

206 Rear translational rod bearing

208 Front translational rod bearing

220 Translation platform

250 Lead screw

254 Lead screw drive nut

258 Linear drive motor

280 Preload member

282 Inner preload spacer

284 Outer preload spacer

300 Vacuum imaging drum

350 Coating

400 Laser assembly

402 Lasers diode

404 Fiber optic cables

406 Distribution block

450 Writing swath

500 Printhead

610 Front bearing assembly

612 Brazing material

614 WC substrate

616 Diamond wafer

620 Bearing pad housing

660 Rear pad assembly

What is claimed is:
 1. A wear resistant lathe bed scanning apparatus,comprising:a frame; a scanning means mounted for slidable movement insaid frame, said scanning means having first and second end portions; afirst translational rod bearing for supporting said first end portion ofsaid scanning means for slidable movement in said frame, said firsttranslational rod bearing being in sliding contact with a first bearingpad assembly arranged in said first end portion of said scanning means;a second translational rod bearing cooperatively associated with saidfirst translational rod bearing for supporting said second end portionof said scanning means for slidable movement in said frame said secondtranslational rod bearing being in sliding contact with a second bearingpad assembly arranged in said second end portion of said scanning means;wherein each of said first and second translational rod bearingscomprises a central core of hardenable stainless steel and a hard wearresistant coating on said central core; and, wherein each of said firstand second bearing pad assemblies comprises at least one bearing pad,said bearing pad comprising a laminate having a first inner most layerof tungsten carbide and a second outermost layer of a diamond materiallaminated to said first innermost layer, said second outermost layerdefining a bearing contact surface; and, drive means operably connectedto said scanning means for providing movement of said scanning meansalong said first and second translational rod bearings in said frame. 2.The apparatus recited in claim 1, wherein said diamond is laminated tosaid first innermost layer of tungsten carbide by an epoxy resin.
 3. Theapparatus recited in claim 1, wherein said diamond layer is laminated tosaid first innermost layer of tungsten carbide by silver brazing.
 4. Theapparatus recited in claim 1, wherein said central core comprisingstainless steel having a Rockwell C hardness in the range of about 58 toabout 60, and wherein said stainless steel has coated thereon a titaniumnitride coating layer.
 5. The apparatus recited in claim 1, wherein saidfirst innermost layer of tungsten carbide comprises about 2% to about20% by weight cobalt and has a thickness in the range of about 5 toabout 50 mm.
 6. The apparatus recited in claim 1, wherein said firstinnermost layer of tungsten carbide comprises about 2% to about 20% byweight nickel and has a thickness in the range of about 5 to about 50mm.
 7. Method of moving a scanning element along a frame, comprising thesteps of:providing the apparatus of claim 1; and, activating said drivemeans thereby causing said scanning element to move along said first andsecond translational rod bearings.